A node device that belongs to a wireless ad-hoc network uses a Hello packet to cause routing information to propagate. As an example, a node device A that belongs to an ad-hoc network illustrated in FIG. 1 generates and periodically broadcasts a Hello packet that includes routing information held by the node device A. Upon receipt of the Hello packet, a node device B compares routing information held by the node device B with information included in the Hello packet and obtains from the Hello packet routing information that the node device B did not hold. In addition, the node device B obtains route quality information from the Hello packet and performs a communication using a route with quality information that is as good as possible. The quality information also includes loop information. In this way, using Hello packets, node devices that belong to an ad-hoc network learn information on a route to another node device in the network and perform a communication using the optimum route that has been obtained. Each node device within the ad-hoc network holds, in a routing table, routes to the other node devices within the ad-hoc network. As an example, the node device A holds, in a routing table, information on a route to each of the node devices within the ad-hoc network other than the node device A. Hence, the node device A may transmit a data packet to a node device C via, for example, the node device B. The node devices used in such an ad-hoc network include a node device that includes, for each ultimate destination of a packet, a weighting table to store weighting information for a node that serves as a relay. In the transferring of a packet, the node device references a weighting table associated with the destination node of the packet so as to specify a node that is a destination to which the packet is relayed.
However, in a method wherein each node device records, in a routing table, routes to the other node devices within an ad-hoc network, an increase in the number of node devices within the network leads to larger-size routing tables. Accordingly, a method has been devised wherein node devices within a network are divided into clusters, and each node device stores, in a routing table, information on routes to the node devices within the same cluster.
As a related art, a wireless communication device has been devised that includes a storage device, a group division device, a communication-route selecting device, and a relay device. The wireless communication device determines, according to route information stored in the storage device, a cluster to which it should belong, and stores the result in the storage device.
Several documents such as International Publication No. 2009/130918 and Japanese Laid-open Patent Publication No. 2003-78530 are known.
A control packet is used in the generating of a cluster. As an example, the wireless communication device that determines a cluster to which it should belong according to route information stored in the storage device, i.e., a device described above as a related art, transmits and receives control packets in joining and leaving a cluster. In the case of unicast-transmission of control packets or flooding of control packets toward all of the node devices within the network, processes of transmitting, receiving, and relaying the control packets lead to a problem of an increased load on the node devices within the network.